Wire ropes consist of multiple strands of metal wire—typically steel—twisted together into a laid rope pattern with a diameter—i.e., gauge—of greater than 3/8 inch. While composite ropes with smaller gauges are referred to as cables or cords, ones with larger gauges that employ several strands of laid rope twisted together—i.e., a cable laid pattern—are known as large gauge wire rope.
There is a wide range of wire ropes available, each of which demonstrates unique characteristics that make it suitable for a specific purpose or application. The following blog post outlines the types available and some of the selection considerations to keep in mind when choosing one for a project.
Wire rope comes in many different forms, with the suitability of each depending on the particular application. Some of the types of wire rope commonly employed include:
This type of wire rope is designed to stabilize loads during lifting operations by preventing rotation, spinning, and twisting. It can be used in a single line or a multi-part system and is often employed in applications where it doesn’t make sense or is impossible to use a tag line, increase sheave sizes, or relocate the dead end of a rope. When using rotation-resistant wire rope, care should be taken when securing the rope ends or attaching fittings to ensure they don’t unlay or kink.
During its manufacture, the strands of this type of wire rope are compacted by a die or rollers. The compacted strands have a smaller outer diameter and a smoother outer surface and demonstrate greater strength and wear resistance than comparable uncompacted strands. Compacted strand wire rope is commonly used on ship and harbor mobile cranes, container bridge cranes, overhead hoists, and more.
Compacted and swaged wire rope differs from the above in that the machine operators run the wire rope through only once it is closed. The strands used in its manufacture can be round or compacted. The advantage of using this type of wire rope is higher strength and wear and crushing resistance.
The application of a plastic coating to a wire rope increases the rope’s resistance to abrasion, wear, and other environmental stresses. However, the coating also decreases the ease to which it can be inspected for repair and replacement. This type of wire rope is often used for high strength applications, such as washing lines, cable locks, and barrier ropes.
This type of wire rope is reinforced by filling the spaces between the strands with plastic. The addition of plastic reduces internal wear and tear and helps make these ropes suitable for heavy lifting.
The core of this type of rope is either filled or coated with plastic to improve resistance to bending fatigue and general wear and tear.
When choosing a wire rope, there are several considerations to keep in mind, including:
Industry professionals employ wire rope in a wide range of applications. Choosing the right type of wire rope requires careful consideration of the requirements and restrictions of the application, including the environment and total load.
If you need selection assistance, turn to Armstrong Alar. With almost three decades of experience working with wire rope, we have the skills and knowledge to help you find the optimal wire rope for your project. Learn more about wire rope on our wire rope page or contact us today with specific questions.
Choosing The Right Wire Rope
With each application, your choices of wire ropes can be many. How do you know which one works best for you? Ropes include a combination of characteristics that give them specific performance abilities. Before you choose, it pays to look closely at each rope’s special characteristics.
All wire ropes feature design characteristic tradeoffs. In most cases, a wire rope cannot increase both fatigue resistance and abrasion resistance. For example, when you increase fatigue resistance by selecting a rope with more wires, the rope will have less abrasion resistance because of its greater number of smaller outer wires. When you need wire rope with greater abrasion resistance, one choice is a rope with fewer (and larger) outer wires to reduce the effects of surface wear. But that means the rope’s fatigue resistance will decrease. That’s why you need to choose your wire rope like you would any other machine. Very carefully. You must consider all operating conditions and rope characteristics.
How do you choose the wire rope that’s best suited for your job? Following are the most common characteristics to be considered when selecting a rope for an application.
Wire rope strength is usually measured in tons of 2,000 lbs. In published material, wire rope strength is shown as minimum breaking force (MBF) or nominal (catalog) strength. These refer to calculated strength figures that have been accepted by the wire rope industry. When placed under tension on a test device, a new rope should break at a figure equal to – or higher than – the minimum breaking force shown for that rope. Certain standards allow for an acceptance strength that is 97.5% of the nominal strength to allow for testing variables. The values in this handbook apply to new, unused rope. A rope should never operate at – or near – the minimum breaking force. During its useful life, a rope loses strength gradually due to natural causes such as surface wear and metal fatigue.
Fatigue resistance involves metal fatigue of the wires that make up a rope. To have high fatigue resistance, wires must be capable of bending repeatedly under stress – for example, a rope passing over a sheave.
Increased fatigue resistance is achieved in a rope design by using a large number of wires. It involves both the basic metallurgy and the diameters of wires. In general, a rope made of many wires will have greater fatigue resistance than a same-size rope made of fewer, larger wires because smaller wires have greater ability to bend as the rope passes over sheaves or around drums. To reduce the effects of fatigue, ropes must never bend over sheaves or drums with a diameter so small as to bend wires excessively. There are precise recommendations for sheave and drum sizes to properly accommodate all sizes and types of ropes.
Every rope is subject to metal fatigue from bending stress while in operation, and therefore the rope’s strength gradually diminishes as the rope is used.
Crushing is the effect of external pressure on a rope, which damages it by distorting the cross-section shape of the rope, its strands or core – or all three. Crushing resistance therefore is a rope’s ability to withstand or resist external forces, and is a term generally used to express comparison between ropes. When a rope is damaged by crushing, the wires, strands and core are prevented from moving and adjusting normally during operation. In general, IWRC ropes are more crush resistant than fiber core ropes. Regular lay ropes are more crush resistant than lang lay ropes. Six strand ropes have greater crush resistance than 8 strand ropes or 19 strand ropes. Flex-X® ropes are more crush resistant than standard round-strand ropes.
Metal loss refers to the actual wearing away of metal from the outer wires of a rope, and metal deformation is the changing of the shape of outer wires of a rope. In general, resistance to metal loss by abrasion (usually called “abrasion resistance”) refers to a rope’s ability to withstand metal being worn away along its exterior. This reduces strength of a rope. The most common form of metal deformation is generally called “peening”– since outside wires of a peened rope appear to have been “hammered” along their exposed surface. Peening usually occurs on drums, caused by rope-to-rope contact during spooling of the rope on the drum. It may also occur on sheaves. Peening causes metal fatigue, which in turn may cause wire failure. The hammering – which causes the metal of the wire to flow into a new shape – realigns the grain structure of the metal, thereby affecting its fatigue resistance. The out-of-round shape also impairs wire movement when the rope bends.
When a load is placed on a rope, torque is created within the rope as wires and strands try to straighten out. This is normal and the rope is designed to operate with this load-induced torque. However, this torque can cause loads to rotate. Load-induced torque can be reduced by specially designed rotation resistant ropes. In standard 6 and 8 strand ropes, the torques produced by the outer strands and the IWRC is in the same direction and add together. In rotation resistant ropes, the lay of the outer strands is in the opposite direction to the lay of the inner strands, thus the torques produced are in opposite directions and the torques subtract from each other. Depending upon your application, other wire rope characteristics such as stability, bendability or reserve strength may need to be considered.
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